#include "stdio.h"

int main() {
	long i, sign = 1;
	float sum = 0;
	for (i = 1; i <= 100000000; i++)
		if (i % 2 == 1) {
			sum = sum + 1.0 / (sign * i);
			sign = -sign;
		}

	printf("sum=%f", sum * 4);
	return 0;
}